The present invention relates to a method for controlling a position sensorless motor and a control device thereof, and also a method and a device for frequency-to-voltage conversion mainly used for a position sensorless motor, and more particularly to a method and a device which can make accurate positioning control of a motor when controlling by using a counter electromotive force produced in stator coils.
The brushless DC motor is often used in view of its long life and low noise for motor-driven devices and motor-driven mechanisms used in each field of industrial world. For example, the servomotor, the stepping motor and the like are conventionally used as a motor for positioning in order to reciprocate a printing head of an ink-jet printer.
The servomotor has a position sensor and a speed sensor to make positioning by close loop control. On the other hand, the stepping motor makes positioning by open loop control.
The servomotor can provide very accurate positioning control but requires a very accurate sensor and also complex control. Therefore, it has a drawback that its controlling device and the like cost high in manufacturing.
The stepping motor, on the other hand, does not use a sensor of any sorts to make the open loop control. Therefore, the controlling device and the like therefor do not involve a high cost in manufacturing, but there is a drawback that vibrations and noises are liable to occur in use. In this connection, Japanese Patent Application Laid-Open Publication No. Hei 10-52094 proposes a technology that vibrations and noises can be reduced when the stepping motor is driven in position sensorless close loop driving.
The stepping motor of position sensorless drive detects a rotation position of the rotor by virtue of a counter electromotive force produced in stator coils. Therefore, the rotation position of the rotor cannot be detected when the motor is stopped. When the motor is started, synchronized operation is made to excite the stator coils in synchronization with a position command pulse in the same way as the drive of an ordinary stepping motor, and when the counter electromotive force reaches a level sufficient to detect the rotation position of the rotor, the position sensorless operation takes over from the synchronized operation.
In the position control system of the position sensorless motor as shown in FIG. 8, upon receiving a deviation of the present position detected by a rotation position detector from a commanded position, a PI compensator so controls to bring the present position to agree with the commanded position to control the input into the motor.
Where the speed cannot be increased quickly because of a load on the motor, it is necessary to gradually increase a frequency of a position command pulse. In this case, the motor is rotated in synchronization with the position command pulse during the synchronized operation.
But, when the synchronized operation is changed to the position sensorless operation, the motor position agrees with the position command, and a deviation between them becomes xe2x80x9c0xe2x80x9d. When the deviation is xe2x80x9c0xe2x80x9d, the PI compensator has a settled result xe2x80x9c0xe2x80x9d, and the motor has a drive voltage xe2x80x9c0xe2x80x9d. Therefore, the motor speed drops. Then, the output level of the counter electromotive force produced in the stator coils drops, disabling the detection of the rotation position of the rotor. Consequently, there is a possibility that the position sensorless drive cannot be made, and out of synchronism may be caused because the position sensorless drive can not be made.
Even if the out of synchronism could be avoided, the speed is largely changed as shown in FIG. 9. Therefore, after shifting to the position sensorless operation, deviations are accumulated to cause vibrations in the system, and settling time becomes long.
Where the motor decelerates and stops, there may be a drawback that the counter electromotive force produced in the stator coils can not be detected because of the lowering of the motor speed, out of synchronism is caused, and it becomes impossible to stop the motor at the target position.
In view of the circumstances described above, a primary object of the present invention is to provide a method for controlling a position sensorless motor and a control device thereof which can securely drive even a position sensorless motor and stop it at a target position.
For example, an ink-jet printer injects ink to commanded positions while reciprocally moving a printing head to print characters and pictures on a sheet. And the motor for reciprocating the printing head is called a CR control motor, for which a hybrid type stepping motor is used, for example.
One example of a mechanical structure of such a conventional hybrid type stepping motor will be described with reference to FIG. 12 to FIG. 14.
This hybrid type stepping motor has an opening on top and bottom portions of a casing 201, bearings 202, 203 disposed in the openings and a rotation shaft 204 rotatably supported by the bearings 202, 203 as shown in FIG. 12.
A rotor 205 is mounted on the rotation shaft 204. The rotor 205 comprises a magnet 206 which is inserted into and fixed to the be rotation shaft 204, and rotor pole pieces 207, 208 which are inserted into the rotation shaft 204 and fixed to the top and bottom of the magnet 206. The magnet 206 is magnetized in a direction of thickness (axial direction), and the rotor pole pieces 207, 208 are formed of layered steel plates.
A stator 209 is concentrically disposed around the rotor 205, a plurality (six to nine) of stator pole pieces 210 are disposed at equal intervals on the side of the rotor 205 of the stator 209, and each of the stator pole pieces 210 and the rotor 205 are mutually opposed with a space having a predetermined width therebetween. And, a stator coil 211 is wound around the respective stator pole pieces 210.
A plurality (e.g., 6) of small tooth poles 210a are disposed on the leading end of each of the stator pole pieces 210 so to be arranged in right and left directions from the center as shown in FIG. 13 and FIG. 14. And, a large number (e.g., 36) of small tooth poles 207a are formed on the outer periphery of the rotor pole piece 207 as shown in FIG. 13 and FIG. 14. Similarly, a large number (e.g., 36) of small tooth poles 208a are formed on the outer periphery of the rotor pole piece 208 (see FIG. 14). The small tooth poles 207a of the rotor pole piece 207 and the small tooth poles 208a of the rotor pole piece 208 are arranged in a state displaced by a half pitch, namely arranged with a phase displaced by 180xc2x0 in electrical angle from one another.
The stepping motor configured as described above has the rotor 205 rotated by switching an electric current flowed in the stator coils 211 in synchronization with the pulse input from the outside, and its positioning can be made readily, so that its control circuit can be configured with ease. And, the hybrid type stepping motor is suitable as a CR control motor because it can realize an electrically delicate step angle.
Such a stepping motor can have its control circuit configured readily, but an electric current is flowed through the stator coils regardless of the position of the rotor, different from a brushless DC motor or the like, therefore, uneven rotations and noises are caused due to vibrations caused in the rotor. And, in order to prevent the occurrence of out of synchronism, an electric current with an allowance with respect to a load is flowed to the stator coils, resulting in a drawback that the motor generates a large volume of heat.
It has been demanded to provide a method for controlling a stepping motor which can realize smooth rotations and a low noise level through the elimination of vibrations of the rotor. To smoothly rotate the rotor, it is necessary to detect a rotation position of the rotor and to flow an electric current to the stator coils with appropriate timing. To do so, an encoder can be disposed to readily detect a rotation position of the rotor. But, there are drawbacks that it requires a mounting space and an extra cost, and a magnet for the encoder can not be magnetized. Therefore, it is not practical to have an encoder. As a method for detecting a rotation position of the rotor, therefore, it is preferable to adopt a position sensorless method which utilizes a counter electromotive force produced in the stator coils.
On the other hand, in the hybrid type stepping motor, the small tooth poles 207a of the rotor pole piece 207 and the small tooth poles 208a of the rotor pole piece 208 are configured to have their phase xcex81 and phase xcex82 equal to each other as shown in FIG. 14. In FIG. 14, xcex8=xcex81+xcex82 is 360xc2x0 in electrical angle.
Since the rotor pole pieces 207, 208 have such a large number of small tooth poles 207a, 208a, namely 36 of them and are small in size, the phase angle xcex81 and the phase angle xcex82 may not be made equal to each other because of deviations in fabricating accuracy or assembling accuracy. In such a case, a magnetic flux density produced in the space between the rotor 205 and the stator 209 does not become a sine wave but misshaped as indicated by the solid line in FIG. 15(A). As a result, the counter electromotive force produced in the stator coils 211 does not become a sine wave as indicated by the solid line in FIG. 15 (B). Thus, it was found that a period of a plus half cycle and a period of a minus half cycle did not become equal. In FIG. 15, waveforms indicated by the broken lines show a magnetic flux density and a counter electromotive force when xcex81=xcex82.
Therefore, when the position of the rotor is detected according to the counter electromotive force produced in the stator coils and the timing of flowing an electric current to the stator coils is determined according to the detection, the timing of flowing an electric current may become inappropriate due to deviations in the mechanical precision of the motor. And, such a drawback is desired to be solved.
Where the close loop control is conducted by the position sensorless method, the counter electromotive force produced in the stator coils is used to detect the rotational speed of the rotor as described above, and the speed control is made according to the detection. Therefore, there may also be a drawback that the control precision is lowered due to deviations in the mechanical precision of the rotor of the motor. And it is desired to solve such a drawback.
Accordingly, a second object of the present invention is to provide thereof a method for controlling a motor and a controlling device thereof that even when the rotor section of the motor has deviations in the mechanical precision, changeover timing of the energization of stator coils can be detected accurately, and the rotor can be rotated smoothly with a noise level lowered, and even if the rotor section of the motor has deviations in the mechanical precision, the precision of the close loop control can be prevented from lowering, and furthermore, even if the rotor section of the motor has deviations in the mechanical precision, the changeover timing of energization of the stator coils can be detected accurately and the precision of the close loop control can be prevented from lowering.
As described above, in order to control the motor, the position of the rotor is detected by detecting the counter electromotive force produced in the stator coils without using a sensor. But, when a star-connected motor makes the PWM control as a means for varying the motor speed, the counter electromotive force can be detected with ease because a voltage at a connecting point of stator coils of the motor (hereinafter called xe2x80x9cthe stator-coils-connecting-point-voltagexe2x80x9d becomes about one half of the power voltage in the period that PWM is ON, but the detection becomes difficult in the period that PWM is OFF because the stator-coils-connecting-point voltage of the motor becomes a positive potential or negative potential of the motor applied voltage.
Therefore, when the PWM control is performed, it is necessary to detect the counter electromotive force after removing an influence of PWM.
To do this, there are proposed a method of processing a terminal voltage with a low pass filter, a method of detecting the counter electromotive force only when PWM is ON, and a method of stabilizing the midpoint voltage of the motor by simultaneously turning ON/OFF the positive and negative switching devices.
According to the aforesaid method using the low pass filter, the terminal voltage is passed through the low pass filter and delayed by 90 degrees. Therefore, it has an advantage that the commutation timing can be obtained without providing a separate delay circuit. But, a filter output waveform is deformed due to a spike voltage appearing in the motor terminal voltage immediately after the commutation. Therefore, there is a disadvantage that when the motor load is increased and the period in which the spike voltage is caused becomes long, the commutation cannot be made accurately.
The method which detects the counter electromotive force only when PWM is ON can accurately perform the commutation even if the motor load is increased, by prohibiting the detection of the counter electromotive force in the period that the spike voltage is caused and the period that the PWM is OFF. But, it has a disadvantage that the circuit scale becomes large because a circuit for prohibiting the detection of the counter electromotive force is required and a drawback that the detection is delayed if the PWM frequency is not high enough. Besides, there are drawbacks that the stator-coils-connecting-point voltage is varied largely while PWM is OFF, so that the voltage of the no exiting phase is also changed largely, and a resonance current flows between the output capacitance of the switching device and the motor coil, disabling the accurate detection of the counter electromotive force.
The method which turns ON/OFF the plus and minus switching devices simultaneously is described in, for example, Japanese Patent Application Laid-Open Publication No. Sho 59-172991 or No. Hei 2-20636. Japanese Patent Application Laid-Open Publication No. Sho 59-172991 processes a terminal voltage with the low pass filter and therefore has a problem that the commutation cannot be made accurately because of the increase of the motor load. And, Japanese Patent Application Laid-Open Publication No. Hei 2-20636 needs to input the stator-coils-connecting-point potential of the terminal voltage to the filter and therefore has a drawback that the motor cost increases because it is necessary to have a line to enter the stator-coils-connecting-point potential from the motor in addition to the problem of the increase in the motor load.
Accordingly, a third object of the present invention is to provide a motor drive device which can make accurate commutation without being affected by a change in the motor load or the PWM frequency.
A conventional motor control device for driving a motor is provided with a frequency-to-voltage conversion device which can obtain a DC voltage proportional to the frequency of an input signal in order to control the motor speed.
An example of such an analog type frequency-to-voltage conversion device comprises a one-shot multiple-vibrator 401 and an RC filter 402 consisting of a resistor R and a capacitor C as shown in FIG. 32.
In the frequency-to-voltage conversion device configured as described above, for example a pulse output from a motor rotation detector is converted into a duty ratio corresponding to the rotational speed by the one-shot multiple-vibrator 401 and smoothed by the RC filter 402. Thus, there is obtained a DC voltage as shown in the drawing.
But, the conventional frequency-to-voltage conversion device has a drawback that output is delayed because it has a filter element such as the RC filter 402 to reduce an output ripple.
When a high resolution encoder can be used as the aforesaid motor rotation detector, the delay of output can be decreased because the output ripple can be made small even by making a time constant of the RC filter 402 small.
But, when a position sensorless operation of a brushless DC motor for example is performed to make commutation by detecting the counter electromotive force produced in its stator coils, it is difficult to enhance the detection resolving power, so that it is necessary to increase a time constant of the RC filter 402 in order to decrease the output ripple of the conventional frequency-to-voltage conversion device. Therefore, when the conventional frequency-to-voltage conversion device is used for the position sensorless drive type motor to make the close loop control, there is a drawback that responsivity can not be improved due to an influence of the delay in output from the RC filter 402.
And, where the position sensorless drive is conducted, the counter electromotive force is not produced in the stator coils when the motor is not operating. Then, the position of the rotor cannot be detected. Accordingly, it is forced to make commutation by making the synchronized operation to start the motor, which is then accelerated until a detectable counter electromotive force is produced in the stator coils, and the shift to the position sensorless drive is made.
In a low speed rotation region before shifting to the position sensorless drive, the motor is driven in the synchronized operation, namely in an open loop, and the close loop control is not made. Thus, where the control is performed in a predetermined rotation range only or a controllable operation range is limited, the conventional frequency-to-voltage conversion device can provide power in a rotation range outside the necessary range. Therefore, it has drawbacks that there is a large volume of waste and a dynamic range of the frequency-to-voltage conversion output cannot be made wide.
Therefore, a fourth object of the invention is to provide a frequency-to-voltage conversion method and its device by which output is not delayed, linearity to the rotational speed in the output range can be secured, and a wide dynamic range can be obtained; and
also a motor control device which serves to improve responsivity.
The present invention is a method for controlling a position sensorless motor which is provided with a synchronized operation and a position sensorless operation and has operation mode-switching means for switching between such operations, which comprises the steps of:
exciting stator coils of the motor in synchronization with a position command signal during the synchronized operation to rotate the rotor;
detecting a rotation position of the rotor based on counter electromotive forces produced in the stator coils during the position sensorless operation, exciting the stator coils in synchronization with the detected rotation position of the rotor to rotate the rotor, determining a deviation between a target position and the present position from a target rotation position and the detected rotation position according to the position command signal, and making a position sensorless close loop drive based on the determined deviation; and
adding a predetermined bias to the deviation at the time of starting the position sensorless operation and then decreasing the bias.
The invention is also the method for controlling a position sensorless motor, wherein switching from the synchronized operation to the position sensorless operation is conducted under a condition that the counter electromotive forces produced in the stator coils have reached a predetermined level, and switching from the position sensorless operation to the synchronized operation is conducted under a condition that the deviation has become zero.
The invention is a device for controlling a position sensorless motor which is provided with a synchronized operation and a position sensorless operation and has an operation mode-switching means for switching between such operations, which comprises:
stator coil drive means which excites stator coils of the motor in synchronization with a position command signal when the synchronized operation is selected by the operation mode-switching means and, when the position sensorless operation is selected, detects the rotation position of the rotor based on counter electromotive forces produced in the stator coils, and excites the stator coils in synchronization with the detected rotation position of the rotor;
deviation calculation means which determines a deviation between a target position and the present position from the position command signal and the detected rotation position of the rotor when the position sensorless operation is selected by the operation mode-switching means;
control means which controls the drive of the stator coil drive means according to the deviation determined by the deviation calculation means when the position sensorless operation is selected by the operation mode-switching means; and
bias control means which adds a predetermined bias to the deviation determined by the deviation calculation means immediately after the selection of the position sensorless operation by the operation mode-switching means and decreases the bias with a lapse of time.
And, the invention is the device for controlling a position sensorless motor, wherein the operation mode-switching means has frequency measuring means for measuring a frequency of the position command signal, switches from the synchronized operation to the position sensorless operation when a frequency of the position command signal exceeds a predetermined value, and switches the position sensorless operation to the synchronized operation when the deviation becomes zero.
The invention is also a method for controlling a position sensorless motor which is provided with a synchronized operation and a position sensorless operation and has an operation mode-switching means for switching between such operations, which comprises the steps of:
exciting stator coils of the motor in synchronization with a position command signal during the synchronized operation to rotate a rotor;
detecting a rotation position of the rotor based on counter electromotive forces produced in the stator coils during the position sensorless operation, exciting the stator coils in synchronization with a rotor rotation position signal indicating the detected rotation position of the rotor to rotate the rotor;
determining a deviation between a target position and the present position from a target rotation position and the detected rotation position of the rotor according to the position command signal, adding an integral value of the determined deviation to the deviation, determining a rotor rotational speed on the basis of the rotor rotation position signal, making position sensorless close loop drive on the basis of a value obtained by subtracting the rotor rotational speed from an added value of the deviation and the integral value of the deviation; and
setting a predetermined initial value for the integral value of the deviation when the synchronized operation is switched to the position sensorless operation by the operation mode-switching means.
And, the invention is the method for controlling a position sensorless motor, wherein:
the operation mode-switching means has frequency measuring means for measuring a frequency of the position command signal; and
the operation mode-switching means changes the operation mode to the position sensorless operation when a frequency of the position command signal or a counter electromotive force level exceeds a first predetermined value after starting the synchronized operation, and changes the position sensorless operation to the synchronized operation when the frequency of the position command signal or the counter electromotive force level becomes lower than a second predetermined value and the deviation is zero.
The invention is also a device for controlling a position sensorless motor which is provided with a synchronized operation and a position sensorless operation and has an operation mode-switching means for switching between such operations, which comprises:
stator coil drive means which excites stator coils of the motor in synchronization with a position command signal when the synchronized operation is selected by the operation mode-switching means and, when the position sensorless operation is selected, detects the rotation position of the rotor based on counter electromotive forces produced in the stator coils to excite the stator coils in synchronization with a rotor rotation position signal indicating the detected rotation position of the rotor;
deviation calculation means which determines a deviation between a target position and the present position from a target rotation position according to the position command signal and the detected rotation position of the rotor when the position sensorless operation is selected by the operation mode-switching means;
integration means for determining an integral value of the deviation determined by the deviation calculation means;
rotational speed detection means for determining a rotor rotational speed on the basis of the rotor rotation position signal;
control means which controls the drive of the stator coil drive means on the basis of a value obtained by adding an integral value of the deviation to the deviation and subtracting the rotor rotational speed from the added value of the deviation and the integral value of the deviation; and
initial value setting means for setting a predetermined initial value as the integral value of the deviation by the integration means when the synchronized operation is changed to the position sensorless operation by means of the operation mode-switching means.
And the invention is the device for controlling a position sensorless motor, wherein the operation mode-switching means has frequency measuring means for measuring a frequency of the position command signal, changes the synchronized operation to the position sensorless operation when the frequency of the position command signal or a counter electromotive force level exceeds a first predetermined value, and changes the position sensorless operation to the synchronized operation when the frequency of the position command signal or the counter electromotive force level becomes lower than a second predetermined value and the deviation is zero.
The invention is also a method for controlling a motor which detects a moment of changing a counter electromotive force produced in stator coils of the motor from plus to minus or from minus to plus, decides changeover timing of energizing the stator coils by adding a delay time with reference to the respective detected moments, and flows an electric current to the stator coils on the basis of the decided changeover timing of energization to rotate the rotor, characterized in that the delay time is a measuring time which is among measuring times obtained by measuring a time between the respective detected moments and corresponds to a positive or negative period of the counter electromotive forces.
And the invention is the method for controlling a position sensorless motor, wherein the delay time is a time obtained by sequentially measured times between the respective detected moments and using the time which is the time measured earlier by one immediately before the decision of the changeover time for energization.
The invention is also a device for controlling a position sensorless motor, which comprises:
position detection means for producing a rotor position signal indicating a rotation position of a rotor by comparing counter electromotive forces produced in stator coils of the motor with a predetermined voltage;
clocking means for detecting a moment of change in the rotor position signal produced by the position detection means and measuring a time between the detected moments of changes;
energization changeover timing decision means which adds a delay time with reference to the moments of changes detected by the clocking means to decide the energization changeover timing of the stator coils and uses as the delay time the measured time corresponding to the positive and negative periods of the counter electromotive forces among the measured times by the clocking means; and
exciting means for flowing an electric current to the stator coils with the energization changeover timing decided by the energization changeover timing decision means.
And the invention is the device for controlling a position sensorless motor, wherein:
the clocking means sequentially detects rising and falling edges of the rotor position signal produced by the position detection means and sequentially measures a time between the detected edges; and
the energization changeover timing decision means, when respective edges are detected by the clocking means, decides the energization changeover timing of the stator coils by adding a delay time with reference to the respective moments of detection and uses as the delay time the time which is the time measured earlier by one immediately before the decision of the energization changeover timing by means of the clocking means.
The invention is also a method for controlling a position sensorless motor which detects a position of a rotor by virtue of counter electromotive forces produced in stator coils of the motor and rotates the rotor by flowing an electric current to the stator coils on the basis of the detected position, characterized in that:
a moment of change of the counter electromotive force from plus to minus or from minus to plus is detected, a time between the detected moments of change is measured, a rotational speed of the rotor is determined from the average of two times corresponding to the plus and minus periods of the counter electromotive force among the measured times, and close loop control is performed according to the determined rotational speed.
The invention is also a method for controlling a position sensorless motor which detects a position of a rotor by virtue of counter electromotive forces produced in stator coils of the motor and rotates the rotor by flowing an electric current to the stator coils on the basis of the detected position, characterized in that:
a moment of change of the counter electromotive force from plus to minus or from minus to plus is detected, a time between the detected moments of change is measured, a rotational speed of the rotor is determined at the every moment of change from the average of the last measured time and the measured time before last, and close loop control is made according to the determined rotational speed.
The invention is also a device for controlling a motor, which comprises:
position detection means for producing a rotor position signal indicating a rotation position of a rotor by comparing counter electromotive forces produced in stator coils of the motor with a predetermined voltage;
exciting means for flowing an electric current to the stator coils on the basis of the rotor position signal produced by the position detection means;
rotational speed detection means which sequentially detects a moment of the change from the rotor position signal produced by the position detection means, measures a time between the detected moments of the change, and determines a rotational speed of the rotor from the average of the two times corresponding to the plus and minus periods of the counter electromotive forces among the measured times; and
control means for controlling the exciting means so to have the rotational speed determined by the rotational speed detection means agreed with a target value.
The invention is also a device for controlling a position sensorless motor, which comprising:
position detection means for producing a rotor position signal indicating a rotation position of a rotor by comparing counter electromotive forces produced in stator coils of the motor with a predetermined voltage;
clocking means which detects a moment of change of the rotor position signal produced by the position detection means and measures a time between the detected moments of change;
energization changeover timing decision means which adds a delay time with reference to the moments of change detected by the clocking means to decide the energization changeover timing of the stator coils and uses as the delay time the time corresponding to the plus and minus periods of the counter electromotive forces among the times measured by the clocking means;
exciting means for flowing an electric current to the stator coils with the energization changeover timing decided by the energization changeover timing decision means;
rotational speed detection means which determines the rotational speed of the rotor from the average of the two times corresponding to the plus and minus periods of the counter electromotive forces among the times measured by the clocking means; and
control means for controlling the exciting means so to have the rotational speed determined by the rotational speed detection means agreed with a target value.
The invention is also a device for controlling a position sensorless motor used for a motor having its rotor rotated by causing commutation in star-connected stator coils, comprising an inverter circuit which includes plus side switching devices and minus side switching devices to supply a power voltage to the stator coils, a counter electromotive force detection circuit for detecting counter electromotive forces of the stator coils, and a control circuit for controlling the inverter circuit on the basis of output from the counter electromotive force detection circuit; the control circuit having a PWM circuit which emits a PWM signal, and plus side switching devices and minus side switching devices of the inverter circuit being simultaneously turned ON/OFF according to the PWM signal, wherein:
the counter electromotive force detection circuit is provided with a comparator, and makes the terminal voltages of the stator coil pulsed by inputting the terminal voltages of the stator coils into the comparator directly or after dividing and also inputting the power voltage after dividing, and the terminal voltages of the stator coils and the power voltage are determined to have a voltage division ratio of 2 to 1.
And the invention is the device for controlling a position sensorless motor, wherein the comparator of the counter electromotive force detection circuit has the terminal voltage of the stator coil inputted after divining into (xc2xd) and the power voltage inputted after dividing into (xc2xc).
And the invention is a device for controlling a brushless DC motor, wherein the control circuit has a commutation signal transmission circuit which produces a pulse for causing commutation in the stator coils on the basis of the terminal voltage of the stator coils pulsed by the comparator, and the commutation signal transmission circuit prohibits the detection of the terminal voltage of the stator coils immediately after the commutation.
The invention is also a frequency-to-voltage conversion method which is provided on a rotation control device and generates a predetermined output signal according to an input signal, which comprises the steps of:
fixing a value of the output signal to a predetermined value when the rotational speed determined based on the input signal is not more than a predetermined value, and
generating the value of the output signal in proportion to the rotational speed when the rotational speed is not less than the predetermined value.
The invention is also a frequency-to-voltage conversion method which is provided on a rotation control device and generates a predetermined output voltage according to an input signal, which comprises the steps of:
fixing the output voltage to a minimum value when the rotational speed determined based on the input signal is not more than a predetermined value; and
allocating the output voltage in proportion to the rotational speed within its output range when the rotational speed is in a range not less than the predetermined value.
The invention is also a frequency-to-voltage conversion device, which comprises:
counting means which inputs an input signal from a rotation detector and counts pulses of a predetermined frequency over one cycle of the input signal; and
voltage generation means which fixes an output voltage to a minimum value when a rotational speed corresponding to the counted value by the counting means is not more than a predetermined value and generates the output voltage in proportion to the rotational speed within the output range when the rotational speed is in a range of not less than the predetermined value.
And the invention is the frequency-to-voltage conversion device, wherein the voltage generation means comprises a conversion table in which the counted value by the counting means and its corresponding output voltage are stored in advance.
The invention is also a motor control device, which comprises:
rotor position signal generation means which generates a rotor position signal indicating a rotation position of a rotor on the basis of a counter electromotive force produced in stator coils of a motor;
exciting means for energizing the stator coils on the basis of the rotor position signal generated by the rotor position signal generation means; and
control means for controlling the energization of the exciting means so to follow the rotations of the rotor according to the command; wherein:
the control means has counting means for counting pulses of a predetermined frequency over one cycle of a signal related to the rotations of the rotor generated on the basis of the rotor position signal, and voltage generation means which fixes the output voltage to a minimum value when the rotational speed corresponding to the counted value of the counting means is not more than a predetermined value and generates the output voltage in proportion to the rotational speed within the output range when the rotational speed is in a range of not less than the predetermined value.
And the invention is the motor control device, wherein the voltage generation means comprises a conversion table in which the counted value of the counting means and its corresponding output voltage are stored in advance.
And the invention is the motor control device, wherein the motor is a three-phase hybrid type stepping motor.
The invention is the motor control device, wherein the motor is to be used to drive at least one of a printer head carriage and a printer paper-feeding mechanism.